Blood entering the alimentary tract, unless vomited, will appear ultimately on or within the stools. The longer it stays in the bowel, the more it is broken down and the darker it becomes. Therefore, it can be seen that the appearance of the blood in the rectum is a function of its point of entry (i.e. how far it has to travel) and of its transit time (i.e. how long it takes to traverse the alimentary tract). As a general rule, bleeding from the oesophagus, stomach and duodenum appears as black and tarry stools (melaena), from the small bowel as dark red-brown stools and from the colon as red ‘altered blood’ mixed with the stools. Bleeding from the anorectal region itself appears as bright red streaking on the surface of the stool or on the toilet paper, because the stool has been formed already at the time of contact with the blood.

Blood mixed with diarrhoea is seen in inflammatory conditions of the bowel, particularly colitis and proctitis, which may be caused by acute infection. Bleeding with chronic diarrhoea is more suggestive of inflammatory bowel disease.

Rapid bleeding from the oesophagus, stomach or duodenum may cause a child to vomit bright red blood (haematemesis), which will be observed in association with pallor and signs of shock. With slower bleeding from the upper gastrointestinal tract, the blood becomes altered by the gastric acid to appear as ‘coffee-ground’ vomitus. However, bleeding may occur from these organs without vomiting.

In the neonate, the most common cause of bleeding is an anal fissure, which may result from the passage of a stool or may be iatrogenic and sustained during introduction of a rectal thermometer. Small, bright red streaks of blood can be seen on the stool or as spots on the nappy. The child is otherwise well, feeds normally and has a soft, non-tender abdomen.

The anus should be examined carefully for evidence of a fissure by parting the perianal skin in a lateral direction (Fig. 16.1) with the baby lying supine and hips flexed. It may be helpful to use an assistant to support the legs. A fissure appears as a breach in the mucosa running longitudinally within the anal canal. It is unusual for the examination to make the fissure bleed, and there is rarely evidence of inflammation around it. Therefore, it is easily overlooked unless the perianal skin is stretched well apart and the anal canal inspected carefully. Where a fissure has not been demonstrated adequately, gentle digital examination of the rectum should be performed using the little finger of the right hand, while the left hand supports the legs (Fig. 16.2).

The finger should be gloved and well lubricated to avoid further trauma to the anal canal. Slow withdrawal of the slightly flexed little finger, at the same time as the opposite thumb applies traction to the perianal skin, may further evert the skin and mucosa of the anal canal to expose the anal fissure (Fig. 16.3). Immediately external to the fissure, there may be a mound of redundant skin, the so-called sentinel pile. The fissure cannot be palpated because it is acute, with little inflammation or induration around it, and no fibrosis. It is located most commonly in the midline, posteriorly or anteriorly. The appearance of faeces or blood on the glove should be noted. Introduction of the little finger into the anal canal dilates the canal and in anal fissure may be therapeutic.

Necrotizing enterocolitis is an acquired disease of the newborn where a variable length and distribution of bowel becomes ischaemic and gangrenous. One manifestation of the disease is the passage of blood per rectum (see Chap. 21). In the early stages of enterocolitis, reducing substances may be detected in the stools because absorption of sugars is impaired. Soon, obvious blood is passed rectally. The infant often is premature and has experienced major physiological stress in the perinatal period. The symptoms appear between 3 and 14 days of age. The child rapidly becomes unwell, lethargic and refuses feeds; vomiting may occur. Abdominal distension, if not already present, will develop over the ensuing hours. The abdomen becomes tender, and where there is gangrenous bowel present, the abdominal wall becomes tight, oedematous and red, reflecting the underlying peritonitis. Often, the first indication of necrotizing enterocolitis is the onset of apnoeic spells and bradycardia. The diagnosis is confirmed on plain radiology. In severe cases of necrotizing enterocolitis, frank blood and even blood-stained tissue can be passed rectally.